JP7634420B2 - Image forming device - Google Patents

Description

An embodiment of the present invention relates to an image forming device.

For example, in an electrophotographic image forming apparatus, a heated roller is used to fix a developer attached to a sheet of paper.
If the pressure applied by this roller to the paper and developer is reduced, poor fusing may occur.
In view of these circumstances, it has been desired to reduce the possibility of poor fixing occurring.

JP 2006-242982 A

The problem that this invention aims to solve is to provide an image forming device that can reduce the possibility of poor fixing.

The image forming apparatus of the embodiment includes a heating section, a pressing section, a detection section, a control section, and a setting section. The heating section generates heat to heat the paper conveyed in the conveying direction over the entire area in the direction perpendicular to the conveying direction. The pressing section applies pressure to the paper heated by the heating section over the entire area in the direction perpendicular to the conveying direction. The detection section detects the temperature of the pressing section. The control section controls the heating section so that the temperature detected by the detection section approaches a control temperature. Before starting image formation for one job, the setting section sets a predetermined first temperature as the control temperature when either one of the following two conditions is not met: ( 1 ) the number of sheets on which images are formed in the job is a number predetermined as a large volume print, and (2) the paper used is a paper predetermined as a narrow paper, and sets a predetermined second temperature different from the first temperature as the control temperature when both of the two conditions are met .

FIG. 2 is a diagram illustrating a schematic mechanical configuration of an MFP according to an embodiment. 2 is a block diagram illustrating a configuration related to control of the MFP illustrated in FIG. 1 . FIG. 3 is a block diagram showing a main circuit configuration of a system controller shown in FIG. 2 . 4 is a flowchart of a print control process performed by the processor shown in FIG. 3 . 2 is a graph showing the results of measuring the temperature of the fixing belt shown in FIG. 1 at a plurality of positions in the longitudinal direction of the fixing belt; 2 is a diagram showing the results of measuring the temperature of the press roller shown in FIG. 1 at a plurality of positions in the longitudinal direction of the press roller; 2 is a graph showing the results of measuring the temperature of the fixing belt shown in FIG. 1 at a plurality of positions in the longitudinal direction of the fixing belt; 2 is a diagram showing the results of measuring the temperature of the press roller shown in FIG. 1 at a plurality of positions in the longitudinal direction of the press roller; 2 is a diagram showing the relationship between the control temperature and the print speed and the temperature difference according to the position in the longitudinal direction of the press roller shown in FIG. 1 . 2 is a diagram showing the relationship between the temperature difference and the outer diameter difference according to the position in the longitudinal direction of the press roller shown in FIG. 1 . FIG. 11 is a diagram showing the relationship between the control temperature, the print speed, and the offset level.

The following describes an embodiment with reference to the drawings. Note that in the following embodiment, an MFP (multi-function peripheral) configured to include an image forming device is used as an example. The various operations and processes described below are merely examples, and it is possible to change the order of some of the operations and processes, omit some of the operations and processes, or add other operations and processes as appropriate.

First, the configuration of the MFP according to this embodiment will be described.
FIG. 1 is a diagram illustrating a schematic mechanical configuration of an MFP 100 according to an embodiment.
As shown in FIG. 1, the MFP 100 includes a scanner 101 and a printer 102 .

The scanner 101 reads an image of an original document and generates image data corresponding to the original document. The scanner 101 uses an image sensor, such as a CCD (charge-coupled device) line sensor, to generate image data according to a reflected light image from the reading surface of the original document. The scanner 101 scans an original document placed on a platen with an image sensor that moves along the original document. The scanner 101 may alternatively scan an original document transported by an ADF (auto document feeder) with a fixed image sensor.

The printer 102 forms an image on a medium to be subjected to image formation by an electrophotographic method. The medium is typically print paper such as cut paper. Therefore, in the following description, it is assumed that print paper is used as the medium. However, the medium may be a sheet material made of paper other than cut paper, or a sheet material made of a material other than paper, such as resin, may be used. The printer 102 has a color printing function for printing color images on print paper, and a monochrome printing function for printing monochrome images on print paper. The printer 102 forms a color image by forming element images using developers of three colors, for example, yellow, magenta, and cyan, or four colors including these and black, by superimposing them. The printer 102 also forms a monochrome image by using a developer of, for example, black. The developer is, for example, a toner. The developer may include, for example, a toner and a carrier. However, the printer 102 may have only one of the color printing function and the monochrome printing function.

In the configuration example shown in FIG. 1, the printer 102 includes a paper feed unit 1 , a print engine 2 , a fixing unit 3 , an ADU (automatic double-sided unit) 4 , and a paper discharge tray 5 .
The paper feed unit 1 includes paper feed cassettes 10-1, 10-2, and 10-3, pickup rollers 11-1, 11-2, and 11-3, transport rollers 12-1, 12-2, and 12-3, a transport roller 13, and a registration roller 14.

The paper feed cassettes 10-1, 10-2, and 10-3 store print paper in a stacked state. The print paper stored in each of the paper feed cassettes 10-1, 10-2, and 10-3 may be different types of print paper with different sizes and materials, or may be the same type of print paper. The paper feed unit 1 may also include a manual feed tray.
The pickup rollers 11-1, 11-2, and 11-3 pick up print sheets one by one from the paper feed cassettes 10-1, 10-2, and 10-3, respectively, and feed the picked up print sheets to the transport rollers 12-1, 12-2, and 12-3.
The conveying rollers 12-1, 12-2, and 12-3 feed the print paper fed from the pickup rollers 11-1, 11-2, and 11-3 to the conveying rollers 13 via a conveying path formed by a guide member (not shown) and the like.

The conveying roller 13 further conveys the print paper fed from any one of the conveying rollers 12-1, 12-2, and 12-3, and feeds it to the registration rollers 14.
The registration rollers 14 correct the skew of the print paper and adjust the timing at which the print paper is fed into the print engine 2.
The number of sets of the paper feed cassette, the pickup roller, and the transport roller is not limited to three, and any number of sets may be provided. Also, if a manual feed tray is provided, it is not necessary to provide any set of the paper feed cassette and the pickup roller and the transport roller that form a pair with it.

The print engine 2 includes a belt 20, support rollers 21, 22, and 23, image forming units 24-1, 24-2, 24-3, and 24-4, an exposure unit 25, and a transfer roller .
The belt 20 is endless and is supported by support rollers 21, 22, and 23 so as to maintain the state shown in Fig. 1. The belt 20 rotates counterclockwise in Fig. 1 with the rotation of the support roller 21. The belt 20 temporarily carries a developer image to be formed on a print paper on its outer surface (hereinafter referred to as the image carrying surface). The belt 20 is made of, for example, semiconductive polyimide in view of its heat resistance and abrasion resistance. The movement of the image carrying surface with the rotation of the belt 20 realizes so-called sub-scanning, and the movement direction of the image carrying surface is also called the sub-scanning direction.

Each of the image forming units 24-1 to 24-4 includes a photoconductor, a charger, a developer, a transfer roller, and a cleaner, and has a well-known structure for forming an image by electrophotography in cooperation with the exposure unit 25. The image forming units 24-1 to 24-4 are arranged along the belt 20 with the axial directions of the respective photoconductors parallel to each other. The image forming units 24-1 to 24-4 have the same structure and operation, except for the color of the developer used. The image forming unit 24-1 forms an element image using, for example, a black developer. The image forming unit 24-2 forms an element image using, for example, a cyan developer. The image forming unit 24-3 forms an element image using, for example, a magenta developer. The image forming unit 24-4 forms an element image using, for example, a yellow developer. The image forming units 24-1 to 24-4 make the element images of each color overlap each other on the image bearing surface of the belt 20. As a result, image forming units 24-1 to 24-4 form a color image by superimposing each element image of each color on the image bearing surface of belt 20 at the time when it passes image forming unit 24-1. Although not shown in the figure, developer containers that contain developers of each color are arranged, for example, in the information space of belt 20.

The exposure unit 25 exposes the photoconductors of the image forming units 24-1 to 24-4 according to image data representing elemental images of each color. A laser scanner or an LED (light emitting diode) head is used as the exposure unit 25. If a laser scanner is used, the exposure unit 25 includes, for example, a semiconductor laser element, a polygon mirror, an imaging lens system, and a mirror. In this case, the exposure unit 25 selectively causes a laser beam emitted from the semiconductor laser element according to image data to be incident on each of the photoconductors of the image forming units 24-1 to 24-4 by switching the emission direction using a mirror. The exposure unit 25 also scans the laser beam in the axial direction of the photoconductor (the depth direction in FIG. 1) using a polygon mirror. This scanning of the laser beam is called main scanning, and its direction is called the main scanning direction.

The transfer roller 26 is disposed parallel to the support roller 23, and sandwiches the belt 20 between the support roller 23 and the transfer roller 26. The transfer roller 26 sandwiches the print paper sent out from the registration roller 14 between the transfer roller 26 and the image carrying surface of the belt 20. The transfer roller 26 then transfers the developer image formed on the image carrying surface of the belt 20 to the print paper by using electrostatic force. In other words, the support roller 23 and the transfer roller 26 form a transfer section. There are cases where the developer is not completely transferred to the print paper and remains on the image carrying surface of the belt 20. For this reason, the developer adhering to the image carrying surface of the belt 20 after passing between the support roller 23 and the transfer roller 26 is removed by a cleaner (not shown) before it reaches the image forming unit 24-4.
Thus, the print engine 2 forms an image on the print paper fed by the registration rollers 14 by electrophotography.

The fixing unit 3 fixes the developer onto the print paper sent out from the print engine 2 by melting and pressing the developer onto the print paper. The fixing unit 3 includes a fixing belt 30, a pressure pad 31, a heater 32, a press roller 33, a peeling plate 34, and a temperature sensor 35. Note that the fixing belt 30 and the press roller 33 are shown in cross section on a plane perpendicular to the axis of rotation.

The fixing belt 30 is an endless belt made of, for example, a heat-resistant resin. The fixing belt 30 is supported by a support mechanism (not shown) so as to rotate around a rotation axis extending in the depth direction in FIG. 1. The length of the fixing belt 30 in the direction of the rotation axis is greater than the maximum length (hereinafter referred to as width) of the print paper in the direction perpendicular to the conveying direction of the print paper (the vertical direction in FIG. 1). The outer diameter of the fixing belt 30 is typically smaller than the length in the direction of the rotation axis. Therefore, the direction of the rotation axis is the longitudinal direction of the fixing belt 30. The fixing belt 30 is heated by the heater 32 to heat the print paper and the developer attached to the print paper.
The pressure pad 31 is provided so as to be in contact with the inner surface of the fixing belt 30 , and presses the fixing belt 30 against the press roller 33 .

The heater 32 heats the fixing belt 30. The heater 32 is, for example, an induction heating (IH) heater, but any other type of heater can be used as appropriate. The heater 32 may have only one heat generating element, or may have multiple heat generating elements arranged in the direction of the rotation axis. Thus, the heater 32 generates heat to heat the print paper via the fixing belt 30, and is an example of a heat generating section.

The press roller 33 is provided parallel to the fixing belt 30. The press roller 33 is supported by a support mechanism (not shown) so as to rotate around a rotation axis extending in the depth direction in FIG. 1. The length of the press roller 33 in the rotation axis direction is larger than the maximum width of the print paper. The outer diameter of the press roller 33 is typically smaller than the length in the rotation axis direction. Therefore, the rotation axis direction is the longitudinal direction of the press roller 33. The press roller 33 sandwiches the print paper sent out from the print engine 2 between itself and the fixing belt 30, and sends it out together with the fixing belt 30 to the ADU 4. Thus, the press roller 33 presses the print paper when sandwiching the print paper together with the fixing belt 30 between itself and the pressing pad 31. In other words, the fixing belt 30, the pressing pad 31, and the press roller 33 work together to realize the function of a pressing unit. The press roller 33 is also heated by the heat of the fixing belt 30, and plays a part in the function of heating the developer attached to the print paper.
However, the function as the fixing unit is not limited to the above configuration, and may be any structure as long as it can press the print paper. For example, instead of the fixing belt 30 and the pressure pad 31, a general roller may be used, and at least one of the roller and the press roller 33 may be pressed toward the other roller to realize the function as the pressing unit. Alternatively, instead of the press roller 33, a structure similar to the fixing belt 30 and the pressure pad 31 may be provided to realize the function as the pressing unit. Furthermore, for example, the function as the pressing unit may be realized by a structure in which the print paper passes between a roller and a fixed plate that are in contact with each other, and the roller and the fixed plate may realize the function as the pressing unit.
The printing paper can also be heated in various other ways as appropriate, instead of the way in which the fixing belt 30 and the press roller 33 are heated. For example, instead of the heater 32, or in addition to the heater 32, a heater may be provided so as to directly heat the press roller 33. Alternatively, instead of the heater 32, or in addition to the heater 32, a heater may be provided so as to directly heat the printing paper before it is sandwiched between the fixing belt 30 and the press roller 33. In these cases, the heater provided instead of the heater 32, or in addition to the heater 32, also corresponds to a heat generating section.

The peeling plate 34 peels the print paper that has passed between the fixing belt 30 and the press roller 33 from the fixing belt 30 , and prevents the print paper from being wound up in the fixing belt 30 .
The temperature sensor 35 measures the temperature of the fixing belt 30. The temperature sensor 35 is typically disposed so as to measure the temperature of the fixing belt 30 near the center in the longitudinal direction. The temperature sensor 35 is an example of a detection unit. However, the temperature sensor 35 may be disposed in any manner as long as it can measure the temperature of the fixing belt 30. The temperature sensor 35 may be disposed so as to measure the temperature of the heater 32, the temperature of the press roller 33, or the temperature around the fixing belt or the press roller 33. In other words, the detection unit may be realized so as to directly detect the temperature of the pressing unit, or indirectly detect the temperature.

The ADU 4 includes a number of rollers and selectively performs the following two operations. In the first operation, the print paper that has passed through the fixing unit 3 is sent directly toward the paper discharge tray 5. This first operation is performed when single-sided printing or double-sided printing is completed. In the second operation, the print paper that has passed through the fixing unit 3 is once transported toward the paper discharge tray 5 side, and then switched back and sent to the print engine 2. This second operation is performed when image formation on only one side of double-sided printing is completed.
The paper discharge tray 5 receives the print paper on which an image has been formed and discharged.

Fig. 2 is a block diagram showing a schematic configuration relating to control of the MFP 100. In Fig. 2, the same elements as those shown in Fig. 1 are given the same reference numerals, and detailed description thereof will be omitted.
In addition to the scanner 101 and printer 102 , the MFP 100 also includes a communication unit 103 , a system controller 104 , and an operation panel 105 .

The communication unit 103 performs processing for communicating with information terminals such as computers and image terminals such as facsimile machines via communication networks such as a local area network (LAN) and a public communication network.
The system controller 104 comprehensively controls each component of the MFP 100 in order to realize the desired operation of the MFP 100. The desired operation of the MFP 100 is, for example, an operation for realizing various functions realized by an existing MFP.
The operation panel 105 includes an input device and a display device. An operator inputs instructions to the operation panel 105 using the input device. The operation panel 105 displays various information to be notified to the operator using the display device. For example, a touch panel can be used as the operation panel 105.

The above-mentioned fixing unit 3, ADU 4, image forming units 24-1 to 24-4, exposure unit 25, and transfer roller 26 that are included in the printer 102 are elements to be controlled. In addition to these, the printer 102 also includes a motor group 6 as an element to be controlled. The motor group 6 includes at least one of the pickup rollers 11-1, 11-2, and 11-3, the transport rollers 12-1, 12-2, and 12-3, the transport roller 13, the registration roller 14, the support roller 21, the transfer roller 26, the fixing belt 30, and the press roller 33, as well as multiple motors for rotating the rollers included in the ADU 4.

The printer 102 further includes a sensor group 7 , a printer controller 81 , a formation controller 82 , an exposure controller 83 , a transfer controller 84 , a fusing controller 85 , an inversion controller 86 , and a motor controller 87 .
The sensor group 7 includes various sensors for monitoring the operating state of the device.
The printer controller 81 , under the control of the system controller 104 , comprehensively controls each component of the printer 102 in order to realize the desired operation of the printer 102 .

The formation controller 82, exposure controller 83, transfer controller 84, fixing controller 85, reversal controller 86, and motor controller 87 all operate under the control of the printer controller 81, and control the operation of the image forming units 24-1 to 24-4, exposure unit 25, transfer roller 26, ADU 4, and motor group 6, respectively. The fixing controller 85 has a function to control the heat generation of the heater 32 so that the temperature measured by the temperature sensor 35 approaches the control temperature by adjusting the driving power supplied to the heater 32, for example. However, the fixing controller 85 controls the entire heater 32 collectively. In other words, the fixing controller 85 does not have a function to control the temperature of the heater 32 individually in each of the multiple regions in the longitudinal direction of the fixing belt 30. In other words, the fixing controller 85 has a function as a control unit.

FIG. 3 is a block diagram showing the main circuit configuration of the system controller 104.
The system controller 104 includes a processor 1041 , a main memory 1042 , an auxiliary storage unit 1043 , an interface unit 1044 , and a transmission path 1045 .

The processor 1041, main memory 1042, and auxiliary storage unit 1043 are connected via a transmission line 1045 to constitute a computer that performs information processing for the above control.
The processor 1041 corresponds to the central part of the computer. The processor 1041 executes information processing (to be described later) in accordance with information processing programs such as an operating system, middleware, and application programs.

The main memory 1042 corresponds to the main storage portion of the computer. The main memory 1042 includes a non-volatile memory area and a volatile memory area. The main memory 1042 stores information processing programs in the non-volatile memory area. The main memory 1042 may also store data required for the processor 1041 to execute processes for controlling each part in the non-volatile or volatile memory area. The main memory 1042 uses the volatile memory area as a work area where data is appropriately rewritten by the processor 1041.

The auxiliary memory unit 1043 corresponds to the auxiliary memory portion of the computer. As the auxiliary memory unit 1043, for example, well-known storage devices such as an EEPROM (electrical erasable programmable read-only memory), a HDD (hard disk drive), and an SSD (solid state drive) can be used alone or in combination. The auxiliary memory unit 1043 stores data used by the processor 1041 when performing various processes and data generated by the processes in the processor 1041. The auxiliary memory unit 1043 stores an information processing program.

The interface unit 1044 performs well-known processing for transmitting and receiving data between the scanner 101, the printer 102, the communication unit 103, the system controller 104, and the operation panel 105. As the interface unit 1044, well-known interface devices or communication devices can be used alone or in combination.
The transmission path 1045 includes an address bus, a data bus, and control signal lines, and transmits data and control signals between the connected components.

Next, the operation of the MFP 100 configured as described above will be described. Note that the following description will focus on operations that differ from the operations of other existing MFPs, and descriptions of other operations will be omitted.

When a request is made to start a job such as copying that involves printing on the printer 102, the processor 1041 in the system controller 104 executes information processing for controlling the printer 102 (hereinafter referred to as print control processing) in accordance with an application program. In the following, the job requested here is referred to as the target job.

FIG. 4 is a flowchart showing the print control process performed by the processor 1041.
In ACT 1, the processor 1041 imports print data. For example, if the target job is copying, the processor 1041 makes the scanner 101 read the document, and imports the print data generated thereby from the scanner 101. Also, for example, if the target job is network printing or facsimile reception, the processor 1041 makes the communication unit 103 receive the print data. The processor 1041 acquires all the print data to be printed in the target job.

In ACT 2, the processor 1041 determines the print paper to be used. For example, if automatic paper selection is specified, the processor 1041 determines the size of the document represented by the print data acquired in ACT 1, and sets the print paper suitable for printing a document of that size as the print paper to be used. For example, if an operation to specify the print paper to be used is performed by the operator on the operation panel 105, the processor 1041 sets the specified print paper as the print paper to be used.

In ACT 3, the processor 1041 checks whether the print paper to be used is a print paper that has been previously determined as narrow paper. The size of print paper that is to be narrow paper may be determined arbitrarily, for example, by the designer of the MFP 100. However, narrow paper is print paper in which there is a large temperature difference between the area where the print paper contacts the press roller 33 (hereinafter referred to as the contact area) and the area where the print paper does not contact (hereinafter referred to as the non-contact area) in the longitudinal direction of the press roller 33, and poor fixing occurs due to the difference in the outer diameter of the press roller 33.

Here, the fixing failure caused by the difference in the outer diameter of the press roller 33 will be described.
Fig. 5 is a diagram showing the results of measuring the temperature of the fixing belt 30 at a plurality of positions in the longitudinal direction of the fixing belt 30. Fig. 6 is a diagram showing the results of measuring the temperature of the press roller 33 at a plurality of positions in the longitudinal direction of the press roller 33. Note that Figs. 5 and 6 show the results of temperature measurement during printing of the same job.

In both Figures 5 and 6, the dashed curves represent the measurement results when the leading edge of the first sheet of print paper passes between the fixing belt 30 and the press roller 33. In both Figures 5 and 6, the solid curves represent the measurement results when the leading edge of the 50th sheet of print paper passes between the fixing belt 30 and the press roller 33. The width of the print paper used is approximately 1/2 the longitudinal length of the fixing belt 30 and the press roller 33. The print speed and control temperature are both preset as standard values (hereinafter referred to as the standard speed) and temperature (hereinafter referred to as the standard temperature).

5 and 6, as the number of consecutive prints increases, the temperatures at the center of both the fixing belt 30 and the press roller 33 decrease because the print paper absorbs heat when it comes into contact with them.
The press roller 33 has a smaller outer diameter at its longitudinal center than at its longitudinal ends because the thermal expansion of the press roller 33 causes a decrease in the pressing force of the press roller 33 against the fixing belt 30, which may cause fixing failure at the central portion of the press roller 33.

For the reasons mentioned above, such fixing problems are more likely to occur when the print paper is narrower. For example, the designer of the MFP 100 may determine, based on experiments, simulations, or empirical rules, that print paper sizes that cause fixing problems are narrow paper. As an example, it is envisioned that A5 and ST-R print paper sizes, which are 150 mm or less in width, will be defined as narrow paper.

If the print paper to be used corresponds to narrow paper, the processor 1041 judges YES in ACT 3 in FIG. 4 and proceeds to ACT 4.
In ACT 4, the processor 1041 determines the total number of prints in the target job. For example, the processor 1041 checks the number of pages of the document represented by the print data captured in ACT 1, and determines the total number of prints by multiplying the number of pages by the number of prints included in the print data or the number of prints separately specified.

In ACT 5, the processor 1041 checks whether the total number of prints determined in ACT 4 corresponds to a predetermined large quantity of prints. For example, the processor 1041 determines that a print corresponds to a large quantity of prints when the number of prints exceeds a predetermined threshold value that takes into account the relationship between the number of prints and the occurrence of transfer defects. Note that the situation that is determined to correspond to a large quantity of prints, or the specific process by which this determination is made, may be appropriately determined by the designer of the MFP 100, for example, based on experiments, simulations, or empirical rules. For example, the above threshold value may be changed depending on the size of the print paper used.

If the printing does not correspond to large volume printing, the processor 1041 judges NO in ACT 5 and proceeds to ACT 6. If the printing paper to be used is not narrow paper, the processor 1041 judges NO in ACT 3 and proceeds to ACT 6. In other words, the processor 1041 proceeds to ACT 6 in both cases when the printing paper to be used is not narrow paper or when the printing does not correspond to large volume printing.

In ACT 6, the processor 1041 instructs the printer controller 81 to start printing based on the print data acquired in ACT 1. In response to such an instruction from the system controller 104, the printer controller 81 operates each section to print the document represented by the print data on the print paper. This operation may be the same as that performed by another printer of the same type. However, the printer controller 81 instructs the fixing controller 85 to set the control temperature in the fixing unit 3 to the standard temperature. The printer controller 81 also instructs the formation controller 82, the exposure controller 83, the reversal controller 86, and the motor controller 87 to set the print speed to a predetermined standard speed. The standard temperature is typically set separately for monochrome printing and color printing, and the standard temperature for color printing is higher than the standard temperature for monochrome printing. Also, different standard temperatures may be set for each case, such as when performing deceleration printing or when the print paper used is thick paper.

In ACT 7, the processor 1041 waits for the printing instructed to start in ACT 6 to be completed. If the printer controller 81 notifies the processor 1041 that the printing is complete, the processor 1041 determines YES and ends the print control process.

On the other hand, if the print paper used is narrow paper and corresponds to a large volume print, the processor 1041 judges YES in ACT 5 and proceeds to ACT 8.
In ACT8, the processor 1041 instructs the printer controller 81 to change the settings related to the control temperature and the print speed. For example, the processor 1041 instructs the printer controller 81 to change the control temperature to an increased temperature set higher than the standard temperature. Also, the processor 1041 instructs the printer controller 81 to change the print speed to a reduced speed set lower than the standard speed. The increased temperature and the reduced speed may be appropriately determined, for example, by the designer of the MFP 100 based on experiments, simulations, or empirical rules. It is desirable that the increased temperature is a temperature at which the temperature difference in the longitudinal direction of the press roller 33 is reduced to a degree that does not cause fixing failure. It is desirable that the increased temperature is determined to a degree that does not cause deformation or the like in various elements that undergo temperature changes due to heat generation by the heater 32. It is desirable that the reduced speed is determined so that the amount of reduction with respect to the standard speed is kept to a necessary minimum in order to minimize the decrease in productivity. It is desirable that the increased temperature is determined to a temperature higher than any of the multiple standard temperatures when the standard temperature is changed according to the printing conditions as described above. Thus, the processor 1041 executes information processing based on the information processing program, and the computer with the processor 1041 as the central part functions as a setting unit.

In ACT 9, the processor 1041 instructs the printer controller 81 to start printing based on the print data acquired in ACT 1. In response to such instructions from the system controller 104, the printer controller 81 operates each section to print the document represented by the print data on print paper. This operation may be the same as that performed by another printer of the same type, for example. However, the printer controller 81 instructs the fixing controller 85 to increase the controlled temperature in the fixing unit 3. The printer controller 81 also instructs the formation controller 82, exposure controller 83, reversal controller 86, and motor controller 87 to reduce the printing speed.

In ACT 10, the processor 1041 waits for the completion of the printing instructed to start in ACT 9. If the processor 1041 is notified of the completion of the printing from the printer controller 81, the result of the determination is YES, and the process proceeds to ACT 11.
In ACT 11, the processor 1041 instructs the printer controller 81 to return the settings changed in ACT 8 to their original settings. For example, the processor 1041 instructs the printer controller 81 to return the control temperature and print speed to the standard temperature and standard speed. Then, the processor 1041 ends the print control process.
As described above, in the MFP 100, in a large volume of continuous printing using narrow print paper, the control temperature is set to an increased temperature and the print speed is set to a reduced speed.

Fig. 7 is a diagram showing the results of measuring the temperature of the fixing belt 30 at a plurality of positions in the longitudinal direction of the fixing belt 30. Fig. 8 is a diagram showing the results of measuring the temperature of the press roller 33 at a plurality of positions in the longitudinal direction of the press roller 33. Figs. 7 and 8 show the results of temperature measurement during printing of the same job.
7 and 8 are measured under the same conditions as those in FIGS. 5 and 6, except that the control temperature and print speed are changed to increasing temperature and decreasing speed.

The maximum temperature difference of the press roller 33 on the 50th sheet is ΔTB in FIG. 8, which is smaller than ΔTA in FIG. 6. Therefore, the difference in outer diameter according to the longitudinal position of the press roller 33 is kept small compared to when the control temperature and print speed are kept at the standard temperature and standard speed.

FIG. 9 is a diagram showing the relationship between the control temperature and the print speed and the temperature difference according to the position in the longitudinal direction of the press roller 33. In FIG.
9, it can be seen that the temperature difference tends to become smaller as the control temperature increases and as the print speed decreases, and as a result, the temperature difference ΔTB is smaller than the temperature difference ΔTA, as described above.

FIG. 10 is a diagram showing the relationship between the temperature difference and the outer diameter difference according to the position in the longitudinal direction of the press roller 33.
10, it can be seen that the smaller the temperature difference, the smaller the outside diameter difference tends to be. Therefore, by reducing the temperature difference ΔTA as described above, the outside diameter difference according to the position in the longitudinal direction of the press roller 33 is suppressed to be small.
Thus, according to the MFP 100, the variation in pressing force depending on the position in the longitudinal direction of the press roller 33 is reduced, and the possibility of poor fixing can be reduced.

In addition, the MFP 100 does not reduce the print speed if the print paper used is not narrow paper or if the job does not involve large volume printing. Therefore, the print speed is reduced only for some jobs, and the decrease in productivity is kept small.

Furthermore, if the MFP 100 sets the control temperature and print speed to the increased temperature and reduced speed before printing for one job begins, the control temperature and print speed are maintained at the increased temperature and reduced speed until printing for that job is completed. This reduces the possibility of poor fixing occurring in all printing for that job.

FIG. 11 is a diagram showing the relationship between the control temperature, the print speed and the offset level.
It can be seen from Fig. 11 that the offset level tends to be reduced by increasing the control temperature and by reducing the print speed. The offset level is a visual evaluation of the effect on image quality of residual images caused by developer that has adhered to the fixing belt 30 from the print paper and re-adheres to the print paper. If the offset level is, for example, OAA or less, and the residual images are within an acceptable level, it is effective to set the print speed to 50 CPM or less.

This embodiment can be modified in various ways as follows.
4, the processor 1041 may instruct the printer controller 81 to change only the settings related to the control temperature. In other words, the print speed may remain at the standard speed.

After issuing an instruction to start printing in ACT 9, the processor 1041 may change at least one of the control temperature and the print speed for some reason before confirming that printing is complete in ACT 10.

The print control process may be executed by a processor provided in the printer controller 81.

The fixing unit 3 may be modified in any way as long as it has the function of heating and pressing the paper, such as by using a roller instead of the fixing belt 30, or by using a belt instead of the press roller 33.

Each function realized by the processor 1041 through information processing can be realized in part or in whole by hardware that executes information processing not based on a program, such as a logic circuit. Each of the above functions can also be realized by combining hardware such as the above logic circuits with software control.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
The invention as originally claimed in the present application is set forth below.
[Note 1] A heat generating unit that generates heat to heat the paper conveyed in a conveying direction over an entire area in a direction perpendicular to the conveying direction;
a pressing unit that applies pressure to the paper heated by the heat generating unit over an entire area in a direction perpendicular to the conveying direction;
A detection unit that detects the temperature of the pressing unit;
a control unit that controls the heat generating unit so as to bring the temperature detected by the detection unit closer to a control temperature;
a setting unit that sets one of a plurality of different candidate temperatures as the control temperature based on the number of sheets to be imaged and a paper size to be used in one job before starting image formation for the job;
An image forming apparatus comprising:
[Supplementary Note 2] The setting unit further sets an image formation speed according to the candidate temperature to be set as the control temperature.
2. The image forming apparatus according to claim 1.
[Additional Note 3] The setting unit maintains the setting before the start of image formation for one job until the end of the one job.
3. The image forming apparatus according to claim 1 or 2.
[Additional Note 4] The setting unit can determine that the job is in a predetermined large volume print state based on a total number of sheets of image formation, and for a job using paper of a paper size whose width in a direction perpendicular to the transport direction is smaller than a specified width, sets the control temperature to a higher candidate temperature than for other cases.
4. The image forming apparatus according to claim 1 ,
[Additional Note 5] When the number of sheets on which images are formed in one job is greater than a specified number and the width of the sheet size in the direction perpendicular to the conveying direction is smaller than the specified width, the setting unit sets a target speed that is lower than the target speed in other cases.
5. The image forming apparatus according to claim 4.
[Additional Note 6] The pressing unit includes a belt that sandwiches the paper between itself and another member,
The detection unit detects the temperature of the belt.
6. The image forming apparatus according to claim 1 ,

1...paper feed unit, 2...print engine, 3...fixing unit, 4...ADU, 5...paper output tray, 6...motor group, 7...sensor group, 10-1 to 10-3...paper feed cassette, 11-1 to 11-3...pickup roller, 12-1 to 12-3...conveyor roller, 13...conveyor roller, 14...registration roller, 20...belt, 21 to 23...support roller, 24-1 to 24-4...image forming unit, 25...exposure unit, 26...transfer roller, 30...fixing belt, 31...pressure pad, 32...heater, 33...press roller, 34... Peeling plate, 35...temperature sensor, 81...printer controller, 82...formation controller, 83...exposure controller, 84...transfer controller, 85...fixing controller, 86...reversal controller, 87...motor controller, 101...scanner, 102...printer, 103...communication unit, 104...system controller, 105...operation panel, 1041...processor, 1042...main memory, 1043...auxiliary memory unit, 1044...interface unit, 1045...transmission path.

Claims (6)

a heat generating section that generates heat to heat the paper being transported in a transport direction over an entire area in a direction perpendicular to the transport direction;
a pressing unit that applies pressure to the paper heated by the heat generating unit over an entire area in a direction perpendicular to the conveying direction;
A detection unit that detects the temperature of the pressing unit;
a control unit that controls the heat generating unit so that the temperature detected by the detection unit approaches a control temperature;
a setting unit which, before starting image formation for one job, sets a predetermined standard temperature as the control temperature when either one of the following two conditions is not met: (1) the number of sheets on which images are formed in the job is a number predetermined as a large volume print, and (2) the paper used is a paper predetermined as a narrow paper, and sets a predetermined increased temperature higher than the standard temperature as the control temperature when both of the two conditions are met ;
An image forming apparatus comprising: The setting unit further sets a standard speed as an image forming speed when the standard temperature is set as the control temperature , and sets a reduced speed lower than the standard speed as the image forming speed when the increased temperature is set as the control temperature .
The image forming apparatus according to claim 1 . the setting unit maintains the setting before the start of image formation for one job until the end of the one job.
3. The image forming apparatus according to claim 1 or 2. the setting unit defines a sheet of paper having a size whose width in a direction perpendicular to the transport direction is smaller than a specified width as the narrow-width sheet .
The image forming apparatus according to any one of claims 1 to 3. the setting unit determines that the number of sheets for which images have been formed exceeds a predetermined threshold value as being a large quantity of prints .
The image forming apparatus according to claim 4 . the pressing unit includes a belt that sandwiches the paper between itself and another member,
The detection unit detects the temperature of the belt.
The image forming apparatus according to any one of claims 1 to 5.